Chronic constipation is one of the most common symptoms of present-day gastroenterology practice. Mertz et al. [1] showed that dyssynergic defecation constitutes up to 59% of patients with refractory chronic constipation in the United States. According to Rome IV criteria [2], functional defecatory disorder (FDD) is diagnosed in patients with functional constipation or irritable bowel syndrome when impaired defecation is demonstrated by at least two of the following: (1) abnormal balloon expulsion test, (2) abnormal anorectal evacuation pattern on manometry or anal surface electromyography (EMG), and (3) impaired rectal evacuation on imaging.

For a long time, clinicians were focusing on anorectal incoordination for the diagnosis of FDD, although patients can have co-existing anorectal sensory and motor abnormalities. During the balloon expulsion test, abnormal expulsion was attributed predominantly to anorectal muscle incoordination, although abnormalities in rectal sensitivity, anal tone, and anal contractility can contribute to abnormal balloon expulsion test [3].

With the introduction of the London classification in 2020 by the International Anorectal Physiology Working Group (IAPWG) [4], there was a significant improvement in the understanding of various anorectal dysfunctions. Multiple studies have been published based on the same classification for evaluation of anorectal disorders like chronic constipation in Parkinson’s disease [5], functional constipation and fecal incontinence [6], although data on dyssynergic defecation are scarce. This study aimed to characterize the spectrum of anorectal motor and sensory abnormalities in patients with FDD using the London classification.

A total of 550 patients with functional constipation were screened. 424 patients were excluded as they did not meet the Rome IV criteria for FDD. Of the remaining 126 patients, 26 were excluded owing to a prior history of biofeedback therapy, previous pelvic surgery, or refusal to provide consent. The final study cohort comprised 100 patients (Figure 1). The demographic details of the patients are described in Table 1. The median age of patients was 34 (18–78) years. Sixty-four patients were males (64%), and the median duration of constipation was 5 (1–20) years.

Anal hypotension with normal contractility was noted in 9 patients (9%), and anal normotension with hypocontractility in 4 (4%). Abnormal expulsion with dyssynergia was noted in 85 patients (85%), and abnormal expulsion with poor propulsion and dyssynergia was noted in 15 (15%). Four patients had rectal hyposensitivity (4%) and five showed borderline rectal hyposensitivity (5%). None of the patients had absent recto-anal areflexia, abnormal expulsion with normal manometric pattern of recto-anal coordination, abnormal expulsion with poor propulsion, normal expulsion with abnormal manometric pattern of recto-anal coordination, or rectal hypersensitivity (Table 2). 75% (n = 75) of patients had only one type of anorectal dysfunction. However, 23% (n = 23) of patients had two types of anorectal dysfunction, and 2% (n = 2) of patients had three types of anorectal dysfunction (Figure 2).

Also, twelve patients (12%) had a major finding, all patients had a minor finding (100%), and five patients (5%) had an inconclusive finding (Table 3). Since patients could have more than one finding, 20% (n = 20) patients had major and minor findings, 5% (n = 5) patients had minor and inconclusive findings, and 75% (n = 75) patients had only minor findings (Figure 3).

Our study shows that multiple types of anorectal dysfunction can co-exist with dyssynergic defecation. None of our patients had absent RAIR, as we only included patients with dyssynergic defecation and excluded the pediatric population from the study [10]. The multicenter study done by Vollebregt et al. [6] in 309 patients with chronic constipation also showed absent RAIR in only 1.8% patients.

Among patients with disorders of anal tone and contractility, a significant number of patients with dyssynergia had abnormal anal tone and/or contractility. In the study done by Vollebregt et al. [6], 45% patients had abnormality in anal tone and contractility, as opposed to 16% in our study. In our cohort, 14% of patients had anal hypotension, hypocontractility, or both, whereas only 2% had anal hypertension. This suggests that baseline anal pressures may not reliably predict the degree of anal relaxation during defecation. However, further studies with larger sample sizes are required to validate this finding.

All our patients had abnormality in recto-anal coordination, which was expected as the presence of dyssynergia and abnormal balloon expulsion was a mandatory inclusion criterion. For the same reason, none of the patients had abnormal expulsion with normal manometric pattern of recto-anal coordination, abnormal expulsion with poor propulsion, or normal expulsion with abnormal manometric pattern of recto-anal coordination. Whether all these patients respond similarly to biofeedback therapy is a question that warrants further studies.

It is well known that rectal hyposensitivity is associated with the severity of chronic constipation [11]. Rectal hyposensitivity was noted in 4% (n = 4), and borderline rectal hyposensitivity was noted in 5% (n = 5) of patients with dyssynergia in our study. The study by Vollebregt et al. [6] showed that the presence of rectal hyposensitivity and borderline rectal hyposensitivity are 10% and 10.7% respectively, in patients with chronic constipation. It is already known that sensory training with biofeedback therapy and sacral neuromodulation improves outcomes in chronic constipation [12, 13]. Hence, incorporating sensory training alongside biofeedback therapy in patients with rectal hypotension and dyssynergia may enhance treatment outcomes in chronic constipation.

Our study has several strengths. It is among the first studies to classify anorectal dysfunctions in dyssynergic defecation using the London classification. Thorough focus on patients meeting the Rome IV criteria for FDD and prospective design of the study are other strengths. However, there are limitations to consider. The exploratory nature and limited sample size in this study may have led to an underestimation of the true prevalence of rarer anorectal abnormalities. The lack of a control group is another limitation of the study. Also, the study was conducted at a single center, which may restrict the generalizability and external validity of our results.

In conclusion, various other disorders of anorectal function coexist with dyssynergia in patients with FDD. Applying the London classification to reporting helps to uncover aspects of anorectal dysfunction that require attention and were otherwise ignored. In addition, further multi-center studies are warranted to obtain external validation and identify how addressing these aspects of anorectal dysfunction in patients with FDD can influence patient outcomes.